Hematopoietic growth factor (HGF) represents a family of biological molecules such as glycoproteins with important regulatory functions in the processes of proliferation, differentiation, and functional activation of hematopoietic progenitors and mature blood cells. HGF compounds can be potent regulators of blood cell proliferation and development in the bone marrow. They are able to augment hematopoiesis when bone marrow dysfunction exists. Recombinant DNA technology has made it possible to clone the genes responsible for many of these factors.
One example of an HGF is the glycoprotein hormone erythropoietin (EPO). EPO is an essential viability and growth factor for the erythrocytic progenitors. EPO is a member of the family of class I cytokines which fold into a compact globular structure consisting of 4 α-helical bundles. Its molecular mass is 30.4 kDa, although it migrates with an apparent size of 34-38 kDa on SDS-polyacrylamide gels. The peptide core of 165 amino acids suffices for receptor-binding and in vitro stimulation of erythropoiesis, while the carbohydrate portion (40% of the total molecule) is required for the in vivo survival of the hormone. The 4 carbohydrate chains of EPO have been analyzed in detail. The 3 complex-type N-linked oligosaccharides at asparagines 24, 38 and 83 appear involved in stabilizing EPO in circulation. EPO is mainly produced by hepatocytes during the fetal stage. After birth, almost all circulating EPO originates from peritubular fibroblast-like cells located in the cortex of the kidneys. Transcription factors of the GATA-family may be important in the control of the time-specific and tissue-specific expression of the EPO gene. In adults, minor amounts of EPO mRNA are expressed in liver parenchyma, spleen, lung, testis and brain. In brain, EPO exerts neurotrophic and neuroprotective effects, which are separate from the action of circulating EPO on erythropoietic tissues. See e.g., Jelkmann, W., Internal Medicine Vol. 43, No. 8 (August 2004).